A cold-cathode fluorescent lamp used as a light source for backlighting of a liquid crystal display is configured such that cylindrical or plate metal is provided as an electrode in a lighting tube, which has phosphor applied onto the inner surface of a glass tube, mercury and the like is contained therein, and the phosphor is excited by ultraviolet radiation, which is generated by electric discharge in the lighting tube, to provide visible radiation.
As to such a cold-cathode fluorescent lamp, a variety of studies on miniaturization, a smaller diameter, higher intensity, and longer lifetime have been conducted in response to diversity of liquid crystal displays. For example, Japanese Patent Laid-Open No. 1-151148 proposes a cold-cathode fluorescent lamp, in which in order to reduce consumption of mercury in a lamp in high-power electric discharge and to optimize a discharging area of an electrode, a cylindrical electrode made of metal is provided on an end of a lighting tube to obtain longer lifetime.
However, in the cold-cathode fluorescent lamp configured thus, when the lamp has a relatively large current of 5 mA or more and the lighting tube has an extremely small inside diameter of 1 to 6 mm, both of the inner surface and outer surface of the cylindrical electrode are subjected to electric discharge. Thus, electrode sputtering materials generated by electric discharge are increased, thereby accelerating a so-called mercury trapping phenomenon, which consumes mercury in the lamp. Consequently, longer lifetime of the cold-cathode fluorescent lamp cannot be achieved.
The present invention has as its object the provision of a cold-cathode fluorescent lamp which can solve the above-mentioned problem. The cold-cathode fluorescent lamp can suppress sputtering caused by electric discharge and reduce consumption of mercury, thereby achieving longer lifetime.